System and method of illuminating interferometric modulators using backlighting

ABSTRACT

An interferometric modulator array device with backlighting is disclosed. The interferometric modulator array device comprises a plurality of interferometric modulator elements, wherein each of the interferometric modulator elements comprises an optical cavity. The interferometric modulator array includes an optical aperture region, and at least one reflecting element is positioned so as to receive light passing through the optical aperture region and reflect at least a portion of the received light to the cavities of the interferometric modulator elements. In some embodiments, the interferometric modulator elements may be separated from each other such that an optical aperture region is formed between adjacent interferometric modulator elements.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/057,392, filed Feb. 11, 2005, entitled “SYSTEM AND METHOD OFILLUMINATING INTERFEROMETRIC MODULATORS USING BACKLIGHTING,” whichclaims priority benefit under 35 U.S.C. § 119(e) from U.S. ProvisionalPatent Application No. 60/613,536, filed Sep. 27, 2004, entitled “SYSTEMAND METHOD OF ILLUMINATING INTERFEROMETRIC MODULATORS USINGBACKLIGHTING.” The present application incorporates the foregoingdisclosures herein by reference in their entirety.

BACKGROUND

1. Field of the Invention

The invention relates generally to a system and method of illuminating adisplay, and more particularly to a system and method of illuminating adisplay using backlighting and one or more reflecting elements.

2. Description of the Related Art

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and/or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. An interferometricmodulator may comprise a pair of conductive plates, one or both of whichmay be transparent and/or reflective in whole or part and capable ofrelative motion upon application of an appropriate electrical signal.One plate may comprise a stationary layer deposited on a substrate, theother plate may comprise a metallic membrane separated from thestationary layer by an air gap. Such devices have a wide range ofapplications, and it would be beneficial in the art to utilize and/ormodify the characteristics of these types of devices so that theirfeatures can be exploited in improving existing products and creatingnew products that have not yet been developed.

For certain applications, interferometric modulator devices can bearranged in an array configuration to provide a display assembly havingadvantageous operational and performance characteristics. For example,these displays may have rich color characteristics as well as low powerconsumption.

Interferometric modulator devices in such displays operate by reflectinglight and producing optical interference. Interferometric modulatorarrays can operate by modulating ambient light reflected from the array.When ambient light is unavailable or insufficient, however, auxiliarylighting, such as provided by backlighting, is desirable. Thus, systemsand methods for illuminating an interferometric modulator array areneeded.

SUMMARY

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

One embodiment of a spatial light modulator comprises a light-modulatingarray comprising a plurality of light-modulating elements each having acavity defined by first and second optical surfaces wherein the secondoptical surface is movable with respect to the first optical surface.The light-modulating array includes at least one optical apertureregion. The light-modulating array device further comprises at least onereflecting element formed between a substrate and the plurality oflight-modulating elements and configured to receive light passingthrough the optical aperture region and to reflect at least a portion ofthe received light to the cavity. Backlighting is thereby facilitated incertain embodiments.

The at least one reflecting element may comprise at least one ofaluminum, silver, titanium, gold, and copper. In addition, the at leastone reflecting element may have a sloped surface.

The reflecting element may have a substantially convex geometry, or asubstantially concave geometry. Furthermore, the at least one reflectingelement may comprise sections interconnected so as to form a continuousunitary structure extending proximal to a plurality of light-modulatingelements.

The spatial light modulator may further comprise a mask aligned with theat least one reflecting element so as to at least partially obstruct aview of the at least one reflecting element. The mask may comprise atleast a portion of an etalon, and the portion of the etalon may compriseone or more layers of partially reflective material and one or morespacing layers.

In some embodiments, the at least one reflecting element comprises atleast a shaped feature and a reflecting material over the shapedfeature.

The substrate of the light-modulating array may comprise at least onecavity, wherein the at least one reflecting element is formed in thecavity of the substrate. The at least one reflecting element maycomprise a reflective material in substantially particulate formsuspended in a substantially transparent material.

In some embodiments, the plurality of light-modulating elements includea metal layer, wherein the metal layer comprises a plurality ofoptically transmissive apertures. At least some of the light-modulatingelements may be separated from each other so as to form an opticalaperture region therebetween.

One embodiment of a method of manufacturing a spatial light modulatorcomprises forming at least one reflecting element on a substrate, andforming a plurality of light-modulating elements above the at least onereflecting element on the substrate so as to form a light-modulatingarray. Each of the light-modulating elements comprises first and secondoptical surfaces that define a cavity, wherein the second opticalsurface is movable with respect to the first optical surface. Thelight-modulating array has at least one optically transmissive apertureregion. The at least one reflecting element is configured to receivelight through the at least one aperture region and reflect at least aportion of the received light into the cavity.

Forming the at least one reflecting element may comprise depositing atleast one of aluminum, silver, titanium, gold, and copper, and formingthe at least one reflecting element may comprise depositing one or morematerials to form a substantially sloped surface, a substantially convexgeometry, or a substantially concave geometry. In some embodiments,forming the at least one reflecting element comprises forming a shapedbase structure on the substrate, and depositing a reflecting material onthe shaped base structure.

The method may further comprise forming a cavity in the substrate, andforming the at least one reflecting element substantially in the cavityof the substrate. Forming the at least one reflecting element maycomprise depositing a layer of reflecting material on the substrate andsurface treating the layer so as to increase the reflectivity and/orscattering of the reflecting material.

In some embodiments, the method further comprises forming a concealingfeature on the substrate aligned with the at least one reflectingelement so as to conceal the visible presence of the at least onereflecting element. The concealing feature may comprise a mask of atleast one of an absorbing material, a reflective material, and atransmissive material. The concealing feature may comprise a mask layerof at least one of carbon black material, a dye, chromium, andmolybdenum. In some embodiments, the concealing feature comprises ametal film so as to form an etalon comprising the metal film and the atleast one reflecting element. The etalon may be configured to appear toa viewer as a predetermined color.

In one embodiment of the method, forming the at least one reflectingelement comprises depositing a composite material on the substratesurface, wherein the composite material comprises reflective particlessuspended in a substantially transparent material. The compositematerial may be deposited at discrete locations on the substrate surfaceso as to form a plurality of reflecting elements, or the compositematerial may be deposited on the substrate surface as a continuouslayer, thereby forming a single reflecting element structure.

In some embodiments, the light-modulating element comprises aninterferometric modulator element and the light-modulating arraycomprises an interferometric modulator array. In other embodiments,however, other types of light modulators including other types of MEMSstructures may be employed.

One embodiment of a method of backlighting an interferometric modulatorarray comprises positioning a light source proximate a first side of theinterferometric modulator array, and reflecting light from the lightsource to a second opposite side of the interferometric modulator array.In some embodiments, the light is reflected with one or more reflectingelements positioned between a substrate and a plurality ofinterferometric modulator elements formed on the substrate. In addition,the method may further comprise masking the one or more reflectingelements to hide the reflecting element from view, and masking maycomprise forming at least a portion of an etalon between the one or morereflecting elements and a viewer.

In some embodiments of the method, the light is reflected with aplurality of discrete reflecting elements, and the light may bereflected with one or more reflecting elements having sloped surfaces.The light may be reflected with one or more convex reflecting elements,or one or more concave reflecting elements. The light may be reflectedwith one or more reflecting elements comprising at least one ofaluminum, silver, titanium, gold, and copper.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a released position and amovable reflective layer of a second interferometric modulator is in anactuated position.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIG. 6A is a cross section of the device of FIG. 1.

FIG. 6B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 6C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7 is a plan view of an interferometric modulator array showingelectrodes for driving the interferometric modulators.

FIG. 8A is a plan view of one embodiment of an interferometric modulatorarray comprising a plurality of interferometric modulator elementsseparated by aperture regions.

FIG. 8B is a cross-sectional view of the interferometric modulator arrayof FIG. 8A showing illumination by a backlighting element.

FIG. 9A is a cross-sectional view of one embodiment of a reflectingelement comprising more than one material.

FIG. 9B is a cross-sectional view of an embodiment of a convexreflecting element formed in a cavity.

FIG. 9C is a cross-sectional view of an embodiment of a concavereflecting element formed in a cavity.

FIG. 10 is a cross-sectional view of a reflecting element and a maskconfigured to conceal the reflecting element from a viewer.

FIG. 11 is a plan view of an interferometric modulator array showing anupper electrode layer patterned to form a plurality of optical apertureregions for transmission of light therethrough.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As discussed more fully below, in certain preferred embodiments, one ormore reflecting elements may be integrated in a display to directillumination from a back light to nearby interferometric modulatorelements. An interferometric modulator array may include one or moreaperture regions through which illumination from a source of backlighting propagates. The aperture regions may be located betweenadjacent interferometric modulator elements, for example. The one ormore reflecting elements is formed between a substrate and theinterferometric modulator array. The reflecting elements may bepositioned so as to receive light passing through the aperture regionsand reflect the received light into optical cavities of theinterferometric modulators. The reflecting elements may have curved orsloped surfaces that direct light as desired. The reflecting elementsmay comprise reflective materials such as aluminum or silver. In certainembodiments, the reflecting elements may comprise a base material suchas a photoresist and a reflective overlaying material such as aluminumor silver. These reflecting elements may be formed on or in thesubstrate and may be covered by planarization. The efficiency ofbacklighting may be enhanced with such reflecting elements. Thesereflecting elements may also prevent leakage of light through the frontof the display.

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theinvention may be implemented in any device that is configured to displayan image, whether in motion (e.g., video) or stationary (e.g., stillimage), and whether textual or pictorial. More particularly, it iscontemplated that the invention may be implemented in or associated witha variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as thereleased state, the movable layer is positioned at a relatively largedistance from a fixed partially reflective layer. In the secondposition, the movable layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable and highly reflective layer 14 ais illustrated in a released position at a predetermined distance from afixed partially reflective layer 16 a. In the interferometric modulator12 b on the right, the movable highly reflective layer 14 b isillustrated in an actuated position adjacent to the fixed partiallyreflective layer 16 b.

The fixed layers 16 a, 16 b are electrically conductive, partiallytransparent and partially reflective, and may be fabricated, forexample, by depositing one or more layers each of chromium andindium-tin-oxide onto a transparent substrate 20. The layers arepatterned into parallel strips, and may form row electrodes in a displaydevice as described further below. The movable layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes 16 a, 16 b) deposited on top ofposts 18 and an intervening sacrificial material deposited between theposts 18. When the sacrificial material is etched away, the deformablemetal layers are separated from the fixed metal layers by a defined airgap 19. A highly conductive and reflective material such as aluminum maybe used for the deformable layers, and these strips may form columnelectrodes in a display device.

With no applied voltage, the cavity 19 remains between the layers 14 a,16 a and the deformable layer is in a mechanically relaxed state asillustrated by the pixel 12 a in FIG. 1. However, when a potentialdifference is applied to a selected row and column, the capacitor formedat the intersection of the row and column electrodes at thecorresponding pixel becomes charged, and electrostatic forces pull theelectrodes together. If the voltage is high enough, the movable layer isdeformed and is forced against the fixed layer (a dielectric materialwhich is not illustrated in this Figure may be deposited on the fixedlayer to prevent shorting and control the separation distance) asillustrated by the pixel 12 b on the right in FIG. 1. The behavior isthe same regardless of the polarity of the applied potential difference.In this way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application. FIG. 2is a system block diagram illustrating one embodiment of an electronicdevice that may incorporate aspects of the invention. In the exemplaryembodiment, the electronic device includes a processor 21 which may beany general purpose single- or multi-chip microprocessor such as an ARM,Pentium®, Pentium II®, Pentium III®, Pentium IV®, Pentium® Pro, an 8051,a MIPS®, a Power PC®, an ALPHA®, or any special purpose microprocessorsuch as a digital signal processor, microcontroller, or a programmablegate array. As is conventional in the art, the processor 21 may beconfigured to execute one or more software modules. In addition toexecuting an operating system, the processor may be configured toexecute one or more software applications, including a web browser, atelephone application, an email program, or any other softwareapplication.

In one embodiment, the processor 21 is also configured to communicatewith an array controller 22. In one embodiment, the array controller 22includes a row driver circuit 24 and a column driver circuit 26 thatprovide signals to a pixel array 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the released state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not releasecompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the released or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be released areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or releasedpre-existing state. Since each pixel of the interferometric modulator,whether in the actuated or released state, is essentially a capacitorformed by the fixed and moving reflective layers, this stable state canbe held at a voltage within the hysteresis window with almost no powerdissipation. Essentially no current flows into the pixel if the appliedpotential is fixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Releasing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias).

FIG. SB is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or released states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and releases the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and release pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thepresent invention.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 6A-6C illustrate three different embodiments of themoving mirror structure. FIG. 6A is a cross section of the embodiment ofFIG. 1, where a strip of metal material 14 is deposited on orthogonallyextending supports 18. In FIG. 6B, the moveable reflective material 14is attached to supports at the comers only, on tethers 32. In FIG. 6C,the moveable reflective material 14 is suspended from a deformable layer34. This embodiment has benefits because the structural design andmaterials used for the reflective material 14 can be optimized withrespect to the optical properties, and the structural design andmaterials used for the deformable layer 34 can be optimized with respectto desired mechanical properties. The production of various types ofinterferometric devices is described in a variety of publisheddocuments, including, for example, U.S. Published Application2004/0051929. A wide variety of well known techniques may be used toproduce the above described structures involving a series of materialdeposition, patterning, and etching steps.

An “interferometric modulator” such as included, for example, in anarray of interferometric modulators forming a spatial light modulatormay also be referred to herein as an “interferometric modulatorelement.”

FIG. 7 is a top view of an exemplary interferometric modulator array 500on a substantially transparent substrate 554, such as glass. In aprocess such as described above, layers of material are patterned toform lower electrode columns 550A-C and upper electrode rows 552A-C asillustrated in FIG. 7. Although not visible in FIG. 7, optical cavitiesor etalons defined by upper and lower mirror surfaces (not shown) arecreated at the intersection of the row 552A-C and column electrodes550A-C. In the illustrated embodiment, three electrode columns 550A-Cand three electrode rows 552A-C forming nine interferometric modulatorselements 525 are shown, although larger or smaller arrays 500 maycontain more or less interferometric modulators. Alternativeconfigurations are also possible. For example, the interferometricmodulator element 525 need not be the same size and shape and need notbe arranged in vertical columns and horizontal rows. Alternately, thespace occupied by the interferometric modulator element 525 at a givenintersection of a column electrode and a row electrode may insteadcomprise a plurality of interferometric modulator elements smaller indimension than those illustrated.

Additionally, the array 500 could also be fabricated with distinct uppermechanical electrodes, for example, one for each interferometricmodulator 525 instead of a single electrode 552 extending across a rowof interferometric modulators. The discrete upper mechanical electrodescan be electrically contacted through a separate layer, for example.Additionally, portions of the electrodes (e.g., the upper mechanicalelectrodes 552) that connect individual modulators 525 in a row may havea reduced width. Such reduced width electrode portions may provideconnections between the interferometric modulators 525 narrower thanshown in FIG. 7. The narrow electrode portions connecting individualmodulators may be located, for example, at the corners of theinterferometric modulator 525 in some embodiments as discussed morefully below.

As shown in FIG. 7, each column 550A-C is electrically connected to acontact pad 556A-C. Each row 552A-C is also electrically connected to acontact pad 556D-F. Timing and data signals may be connected to thecontact pads 556 to address the interferometric modulator array. Asdescribed above, however, the embodiment illustrated is exemplary innature as other configurations and designs may be employed, such asinterferometric modulator arrays without electrical contacts.

In certain embodiments, backlighting is used to illuminate a displaycomprising at least one interferometric modulator array 500 such asshown in FIG. 8A. In such configurations, the interferometric modulatorarray 500 may be designed to receive illumination from the back, or anon-viewing side of the interferometric modulator array.

In the array 500 shown in FIG. 8A, separations 574 betweeninterferometric modulator elements 525 form optical aperture regions, asseen from a non-viewing side of the array. The part of theinterferometric modulators 525 that is depicted in FIG. 8A correspondsto the mechanical layer 570 that supports the upper mirrors (not shown)as described above in connection with FIGS. 1-6C. This array 500 isfabricated with distinct or separate portions 570 of the uppermechanical electrodes, for example, one for each interferometricmodulator 525, instead of a single electrode strip extending across arow of interferometric modulators as shown in FIG. 7. These portions 570of the mechanical layer are separated so as to form the opticallytransmissive aperture regions or spaces 574 therebetween. The discreteupper mechanical electrodes 570 can be electrically contacted through aseparate layer, for example, as described above.

In the exemplary embodiment illustrated in FIG. 8A, the discreteportions of the upper mechanical electrodes 570 create a grid-likeshaped spacing between the interferometric modulators 525. The opticallytransmissive apertures regions 574 in the upper electrode layer 570 maybe substantially devoid of material and/or these optical apertureregions may comprise material which is substantially opticallytransmissive.

The spaces or aperture regions in the interferometric modulator array500 are not limited to those formed between the pixels in a display andmay include, for example, spaces between a plurality of interferometricmodulator elements corresponding to sub-pixel elements within a pixel.These sub-pixels may be used to provide increased color or grayscalerange in multi-color or gray-scale displays, respectively. In someembodiments, the interferometric modulator array comprises one or moreoptically transmissive aperture region in the mechanical layer andmirror of one or more interferometric modulator elements. As discussedabove, the one or more optically transmissive aperture regions may besubstantially devoid of material and/or these optical aperture regionsmay comprise material which is substantially optically transmissive.

In one embodiment, the interferometric modulator array may comprise oneor more substantially central optically transmissive aperture regions.Certain embodiments of an interferometric modulator device can compriseoptically transmissive aperture regions in a combination of theabove-described locations and configurations, such as opticallytransmissive aperture regions both between adjacent interferometricmodulator elements and in the mechanical layer and mirror of one or moreinterferometric modulator elements.

In one embodiment, the optically transmissive aperture regions 574 havea generally constant width w. The width w may be determined by theminimum features size or other design rules of the fabrication process.In general, the space 574 between adjacent portions of the mechanicallayer 570 for different interferometric modulators 525 is as small aspossible so as to avoid wasting any pixel area. The width w can,however, be different depending, e.g., on the size and design of thedisplay device or other factors and is not limited by the embodimentsdescribed and illustrated herein. For example, the optical apertureregion 574 between distinct portions of the mechanical layer 570 may bemade larger than the minimum size in order to increase the amount oflight that passes through the optical aperture region 574 and that isinjected into the interferometric modulator elements 525. In variousembodiments, the width of the aperture regions 574 ranges from betweenabout 2 μm and 1582 m, although widths outside this range are possible.In addition, the length of the aperture regions 574 ranges from betweenabout 10 μm and 100 μm, although lengths outside this range may beemployed. The width and lengths of the aperture regions 574 need not beconstant and may vary throughout the array, for example, to controllight levels at different locations in the array 500. Accordingly, thesize and shape of the interferometric modulator elements 525 andcorresponding portions of the mechanical layer 570 need not be uniformand may vary. For example, in certain embodiments, the size of theinterferometric modulator elements 525 for different sub-pixels within apixel are dithered to provide increased color or grayscale levels.

FIG. 8B is a cross-sectional view of the interferometric modulator array500 of FIG. 8A, taken along line 8B-8B. FIG. 8B shows one embodimentwherein a backlight 575 is positioned proximate a first, non-viewingside 577 of the interferometric modulator array 500. This backlightsource 575 is configured to spread light upon the different portions ofthe mechanical layer 570 and through optically transmissive apertureregions 574. In certain embodiments, this backlight source 575 iselongated in one or more dimensions. The backlight source 575 shown inFIG. 8B, however, is exemplary, as other types of backlighting sourcesmay be used.

In some embodiments, the backlight source 575 may comprise, for example,discrete light sources such as light emitting diodes. The backlightsource 575 may also comprise a combination of one or more light emittersand optics, such as a waveguide, configured to transfer or propagatelight from the light emitter to the interferometric modulator array 500.An optically transmissive layer extending across the array 500 may, forexample, be used as a waveguide.to couple light to the interferometricmodulators 525. The emitters may be disposed at the edge of thiswaveguide to inject light in the waveguide.

As shown in FIG. 8B, in order to direct light from the backlight source575 to optical cavities 584 in respective interferometric modulators525, one or more light reflecting elements 572 are included in thedisplay. The reflecting element 572 is configured to reflect light fromthe backlight source 575 passing through the optically transmissiveaperture regions 574 between the interferometric modulator elements 525.The reflecting element has a reflecting surface 573 that directs thelight to optical cavities 574 in the interferometric modulators 525. Thelight reflecting element 572 may also be referred to as a “scatteringelement”, wherein the reflecting element 572 is further configured toscatter or deflect light into the optical cavities 574 to fill thecavities with light.

The reflecting element 572 may comprise, for example, a grid-likereflecting element that is aligned with the optically transmissiveaperture regions 574 between columns and rows of interferometric opticalelements 525. This unitary structure 572 may, for example, comprisecolumnar or elongated reflective sections aligned parallel to the rowsand columns of modulators 525. FIG. 8B shows a cross-section of columnaror elongated reflecting sections that form part of such a grid-likereflecting element 572. FIG. 8B shows the reflecting surface 573 of thereflecting element 572 configured to direct light into the opticalcavities of the interferometric modulators 525.

Alternatively, a plurality of reflecting elements 572 comprising, forexample, a plurality of discrete structures such as dots, or separateelongate sections may be used. These discrete structures may comprise,e.g., bumps, mounds, and ridges having a reflective surface. Thereflecting elements 572 may be positioned in a regular (uniform) orirregular (e.g., random) arrangement. The reflecting elements 572 mayhave more complex shapes or geometries as well. For example, a grid-likepattern may be segmented into shapes other than columns and rows (e.g.,“+” or “L” shaped elements). Still other shapes are possible that may ormay not together form a grid-like pattern. As described above, however,in some embodiments, a single reflecting element 572 may be used.

As shown in FIG. 8B, the reflecting element 572 is disposed on asubstrate 554 between the substrate and the interferometric modulatorelements 525. The reflecting element 572 may have sections locatedproximate the optically transmissive aperture regions 574 betweendifferent portions of the mechanical layer 570. Accordingly, thecorresponding sections of the reflecting surface 573 are proximate theoptically transmissive aperture regions 574. In one embodiment, thereflecting element 572 or sections thereof are aligned with the apertureregions 574, and may be visible through the aperture regions when viewedfrom the non-viewing side 577 as shown in FIG. 8A.

The reflecting element 572 is configured to receive light from thebacklight source 575, positioned proximal to the non-viewing or firstside of the interferometric modulator array 500 wherein the mechanicallayer 570 is located (designated by arrow 577), through the opticallytransmissive aperture regions 574, and to reflect the received light toa second side 579 of the interferometric modulator array visible to aviewer. This second side 579 of the interferometric modulator array,which is visible to a viewer, is opposite the first side of theinterferometric modulator array where the backlight source 575 islocated. FIG. 8B additionally shows the optical cavity 584 in eachinterferometric modulator element 525 that is formed between an uppermirror 571 a extending from the mechanical layer 570 and a lower mirror571 b comprising, e.g., a metal layer 578 formed over the substrate 554.As described above, the shape of the reflecting surface 573 on thereflecting element 572 is configured to reflect and/or scatter lightinto the optical cavity 584.

In the embodiment illustrated in FIG. 8B, the reflecting element 572 hasa substantially convex cross-section with respect to the substrate 554.Accordingly, the cross-section of the reflecting element is sloped onopposite sides with portions of the reflecting surface 573 inclinedtoward the aperture region 574 and facing adjacent the optical cavities584. The reflecting surface 573 shown is curved. However, the geometryof the reflecting elements 572 is not limited to that illustrated anddescribed herein as other geometries are contemplated. For example, thereflecting elements may have flat or planar sections that may or may notbe tilted or slanted with respect to the substrate 554. For example, thecross-section may be triangular-shaped. Other shapes are also possible.The cross-section may for example be substantially concave. As describedabove, sections of the reflecting element may be elongated.Alternatively, the sections need not be elongated such as in the case ofmounds, bumps, or dots which may in some embodiments be generallycircularly symmetrical. Alternately, the reflecting elements may have anon-uniform geometry. Also, although the reflective surface 573 is shownas substantially smooth, the reflective surface may be rough. Thereflective surface may be stepped or jagged. As described above,reflection from the reflective surface 573 may be diffuse or specular.

The reflecting elements may also be surface treated to increasereflectivity and scattering attributes. For example, the reflectivesurface 573 can be micro-etched so as to create, for example, moresurface area, roughness, and/or ridges so as to increase thedeflection/scattering of light. Alternately, the reflective surface 573can be micro-etched so as to smooth the reflective surface 573, therebyincreasing the light concentration and possibly improving the uniformityof the backlighting of the interferometric modulator array.

In one embodiment, one or more reflecting elements comprise a materialwith a substantially flat or planar structure and micro-roughness,wherein the reflecting element material may be deposited and formed inone or more layers by a process that includes etching, thermalannealing, and/or radiated curing, for example. The micro-roughness maybe created by micro-etching, control of a deposition process, and/orattributes of the material.

In other embodiments, one or more reflecting elements 572 comprise asubstantially optically transmissive material and a plurality ofreflective particles suspended in the transmissive material. Thereflective particles preferably comprise a material configured toreflect and/or scatter incident light. As discussed above, the one ormore reflecting elements may have a unitary structure such as acontinuous layer and/or the reflecting elements may comprise a pluralityof discrete structures. The reflective layer may comprise asubstantially grid-like pattern in certain embodiments.

The position and structure (e.g., shape) of the reflecting elements 572can be manipulated so as to optimize their effectiveness in directinglight into the interferometric modulator cavities 584. The reflectinglight element 572 may be positioned directly beneath the opticalaperture regions 574 in some embodiments, although the reflectingelement may be located differently as well.

In one embodiment, the reflecting elements 572 are wide enough andshaped so that substantially all light from the backlight 575 passingthrough the aperture regions 574 are reflected into the cavities 584 ofthe interferometric modulator array elements 525. In some embodiments,the width of the reflecting element 572 may vary based upon the size ofthe angular distribution of light from the backlight 575 passing throughthe aperture regions 574. For an uncollimated backlight source (i.e.,coming through the holes through a wide range of angles), the size ofthe reflecting element 572 may be a function of the distance from theaperture region to the reflecting element 572. This distance may bedetermined, for example, by the thickness of the upper mirror 571, thespacing between the mirror 571 and the reflecting element 572. The width(w) of the aperture regions 574 may also be a factor as well as therange of angle of the entering light through the aperture region. Whenlight comes through the apertures 574 at a limited range of angles, thereflecting element may be smaller.

In one embodiment, the reflecting elements 572 have a width ofsubstantially greater than the width w of the aperture regions 574, andpreferably greater than 3w. In one embodiment, the reflecting element572 extends a distance of at least w beyond. either side of thecorresponding aperture region 574.

Extremely wide reflecting elements 572, while effective in blockingstray light, may reduce the amount of pixel area available for thereflective state. Thus, a trade-off exists between selecting widereflecting elements to deflect more light and the pixel area availablefor the reflective state of the interferometric modulator element 525.Reflecting elements 572 may have a width of about 1 μm to about 10 μm.Reflecting elements 572 may have cross-sections with larger or smallerwidths in other embodiments.

The reflecting element 572 may have a height of between about 200Åandabout 1000Å, although values outside this range are possible. The heightmay also vary with different sections of the reflecting element 572located at different positions about an interferometric modulator 525 orat different locations in the array 500 having different heights.

The reflecting element 572 preferably comprises one or more reflectivematerials and may include at least one of aluminum, silver, titanium,gold, and copper, for example. Other materials may be employed.Furthermore, the reflecting elements 572 can be either specular ordiffuse reflecting optical elements.

As discussed above, the reflecting element 572 is formed on thesubstrate 554 between the substrate and the interferometric modulatorelements 525. The substrate 554 may have a thickness of about 200 μm toabout 2 mm, or about 2 mm to about 5 mm, for example, or may be largeror smaller. The reflecting elements 572 are covered by a layer ofsubstantially optically transmissive material such as a planarizationmaterial 582. This layer may have a thickness of about 1 μm, forexample. The spacing between the mirror 571 and the reflecting element572, which is discussed above, is related to the thickness of theplanarization material 582. Other materials may be employed inalternative embodiments.

One or more interferometric modulator elements 525, each comprisingoptical cavities 584, are formed above the planarization material 582.These interferometric modulator elements 525 comprise an optical stack583 formed on the planarization material 582, wherein the optical stack583 comprises an electrode layer 580, a metal layer 578, such as chrome,and an dielectric or oxide layer 576. The electrode layer 580 comprisesa conductive material, such as indium tin oxide (ITO), or zinc oxide(ZnO), for example, and may be substantially optically transmissive orpartially transmissive. The metal layer 578 may comprise a material thatis reflective such as chrome. Other metals may also be employed. Invarious embodiments, the electrode layer 580 has a thickness sufficientto be conductive and the metal layer 578 may have a thickness sufficientto be partially reflective. The electrode layer 580 and metal layer 578may, for example, have thicknesses of about 100Å to about 1 μm, and thedielectric layer 576 may have a thickness of about 100 to 2,000Å. Thedielectric layer may also comprise a multilayer dielectric optical filmin some embodiments. Alternative configurations are also possible. Forexample, layers may be excluded and additional layers may be employed.Furthermore, the thicknesses may be outside the ranges in otherembodiments.

As described above, the mechanical layer 570 supports a mirror 571 overthe electrode, metal, and dielectric layers 580, 578, 576 to form thecavity 584. Other configurations are possible. In some embodiments, asdiscussed above, the mechanical layer 570 and the mirror 571 compriseone or more optically transmissive aperture regions configured to allowlight to pass from the backlight source 575 therethrough and into acavity of a corresponding interferometric modulator element. Also, theelectrode 580 and/or the metal layers 578 may comprise a substantiallytransmissive material and/or may comprise a plurality of substantiallytransmissive apertures so as to allow transmission of light reflectingfrom one or more reflecting elements into a cavity of an interferometricmodulator element. These features are discussed in more detailhereinafter.

The reflecting elements 572 may be formed using a plurality of methodsknown in the technology, and a number of exemplary methods are discussedfurther hereinafter in reference to FIGS. 9A-9C, which illustrate aplurality of exemplary reflecting element structures and formations. Inthe embodiment illustrated in FIG. 9A, the reflecting element 572comprises a shaped feature, e.g., a bump 702, formed of a base materialsuch as a polymer. This shaped feature 702 is covered by an overlaylayer 704 comprising reflecting material such as aluminum. The aluminumlayer 704 may reflect light, for example, with a wavelength in thevisible range. A reflective material other than aluminum may be used,such as, e.g., silver, titanium, gold, or copper. A layer of the basematerial may be deposited and patterned to form the bump 702 or otherdesired shape. A layer of reflective material 704 may be deposited onthe polymer base material to form the reflective overlayer.

In the embodiment illustrated in FIG. 9B, the substrate 554 is etched soas to form a cavity 706 with a substantially rectangular cross-section.A reflecting element 572 is formed in the cavity 706 by depositingreflective material such as metal. A substantially convex geometry, forexample, can be formed in the cavity 706. In one embodiment, the cavityhas a substantially convex surface therein, and a substantially convexgeometry is formed by depositing a reflective material over the convexsurface in the cavity. Other geometries are possible.

In the embodiment illustrated in FIG. 9C, a substantially concave cavity708 is formed in the substrate 554 and a layer of reflecting material isdeposited in the cavity 708 so as to form a substantially concavereflecting element 572. Alternatively, concave or convex surfacefeatures may be formed on the substrate that are not in a cavity, forexample, by etching the substrate and the reflecting material may bedeposited on this shaped surface feature. As noted above, the reflectingelement structures, geometries, as well as position illustrated anddiscussed herein are exemplary in nature and other structures,geometries, and positions are not to be excluded. Exemplary methods offorming a reflecting element as described above may comprise depositionof a material, etching, thermal annealing, radiated curing andcombinations thereof.

As discussed in reference to FIG. 8B, the reflecting elements 572 may becovered by planarization material, which has a thickness of about 1 μm,for example. The planarization material may be applied using a methodsuch as spin-on deposition. Several spin-on deposition materials areavailable that are optically transmissive. Many of these materials canbe “cooked” to form a silicon oxide material which is transparent. Suchspin-on deposition materials are available from Dow Corning, Inc. ofMidland, Mich. and Clariant Life Sciences K.K. of Tokyo, Japan. Theplanarization material could also be a material such as photoresist.Once the planarization material is formed, a planarization process, suchas chemical mechanical polishing (CMP), could be used to planarize thesurface of the planarization material. Alternately, materials other thanplanarization material can be employed and multiple layers can also beused.

FIG. 10 illustrates one embodiment of a reflective element 572 for aninterferometric modulator array wherein a concealing feature or mask isused to hide the reflecting element 572 from view. In one embodiment, amask 802 is formed over the glass substrate 554 and covered by asubstantially transparent layer 804. The reflecting element 572 is thenformed over the transparent mask 802. Preferably, the mask 802 comprisesa material configured to conceal the visible presence of the reflectingelement 572. This mask 802 may be opaque or semi-transparent. The mask802 may comprise an absorbing material, a reflective material, atransmissive material, or a combination thereof, and may comprisematerials such as chromium (Cr), molybdenum (Mo), carbon black, dyes,etc. In certain embodiments, for example, the mask 802 may comprisephotoresist materials (e.g., spin-on resist), polyimides, photoamids,inorganic polymers, and/or polymer materials which are either inherentlysubstantially optically absorptive or reflective or which have amaterial, such as carbon particles (e.g., carbon black), metalparticles, fillers and/or dyes, incorporated therein such that the mask802 is substantially optically absorptive or reflective in the visiblelight spectrum. In certain embodiments, the material(s) are selected andincorporated into the mask 892 in amounts effective to provide theresulting substantially optically absorptive support structure with ablack appearance. Variations in the design are possible.

In one embodiment, the mask 802 comprises an etalon or portion of anetalon. Specifically, one embodiment of the mask 802 comprises a firstpartially reflective/partially transmissive layer, such as a metal layercomprising, e.g., chromium, and at least one layer of cavity or spacingmaterial, such as an oxide or planarization material, so as to form anetalon comprising the first reflective (e.g., metal) layer and thereflecting element 572. In another embodiment, the mask 802 furthercomprises a second reflective layer between the spacing material and thereflecting element 572, wherein an etalon is formed by the first andsecond reflective layers below the reflecting element 572. The firstand/or second etalon reflective layers may comprise the same material asthe metal layer 578 in the optical stack 583. In certain embodiments,the etalon results in a predetermined color at the visible or viewingside of the interferometric modulator array and masks features which areundesirable for viewing.

As described above, the interferometric modulator array 500 can beefficiently illuminated using backlighting. In some embodiments, thelight is collimated so that the light coming off the backlight source575 has a limited range of angles. Preferably, the light is directedstraight between the backlight source 575 and the array 500. The rangeof acceptable angles may depend on the combination of the structuraldimensions. For example, if the aperture width (w) is 10 μm, the widthof the reflecting element is 30 μm, and the distance between the mirrors571 and the reflecting elements 572 is 1 μm, then steep angles (largeangles with respect to the normal to the substrate) of light will beblocked, and other light will be reflected. The light can be collimatedin several manners, depending on the selection of backlight. For examplesome backlight structures can be provided that limit the emitted lightwithin a certain range of angles. Lenses or other collimating optics maybe employed. The backlight 575 can also use a filter or other opticalfilm to eliminate light at extreme angles.

The reflecting element 572 will spread the collimated light from thebacklight 575 to neighboring interferometric modulators. Because thelight will reflect at a large variety of angles from the reflectingelement, light will be provided to several interferometric modulatorsfrom a single reflecting element. Light for a single interferometricmodulator can also come from a plurality of reflecting elements. It isnot necessary, however, that the light provided by the backlightcomprise collimated light.

An SEM image of another embodiment of the interferometric modulatorarray is shown in FIG. 11. In this interferometric modulator array 500,the mechanical layer 570 is patterned to form a plurality of apertureregions 574 surrounding each interferometric modulator element 525.Narrow portions of the electrode layer 570 at comers of the modulatorelements 525 provide electrical connection between the interferometricmodulators, e.g., along a row. These narrow portions of the electrodelayer 570 are disposed proximal to post structures 599 shown in FIG. 11.The plurality of optically transmissive aperture regions 574 enablelight to be propagated to the reflecting element (not shown) such asdescribe above.

Although spatial light modulators comprising arrays of interferometricmodulator elements have been described above, in other embodiments,other types of light-modulating elements that form the light-modulatingarrays may be employed. For example, other types of MEMS structures maybe employed in other embodiments. Other types of structure not based onMEMS technology may also be used in certain embodiments.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

1. A method of manufacturing a spatial light modulator, comprising:forming at least one reflecting element on a substrate; and forming aplurality of light-modulating elements on the substrate above the atleast one reflecting element so as to form an light-modulating array,the light modulating array having at least one optically transmissiveaperture region, each light modulating element comprising first andsecond optical surfaces that define an cavity, said second opticalsurface movable with respect to the first optical surface, wherein theat least one reflecting element is configured to receive light throughthe at least one aperture region and reflect at least a portion of thereceived light into said cavity.
 2. The method of claim 1, whereinforming the at least one reflecting element comprises depositing atleast one of aluminum, silver, titanium, gold, and copper.
 3. The methodof claim 1, wherein forming the at least one reflecting elementcomprises forming a substantially sloped surface.
 4. The method of claim1, wherein forming the at least one reflecting element comprises forminga substantially convex geometry.
 5. The method of claim 1, whereinforming the at least one reflecting element comprises forming asubstantially concave geometry.
 6. The method of claim 1, wherein saidat least one reflecting element is formed on a layer of material formedon said substrate.
 7. The method of claim 1, further comprising forminga concealing feature on the substrate aligned with the at least onereflecting element so as to conceal the visible presence of the at leastone reflecting element.
 8. The method of claim 7, wherein the concealingfeature comprises a mask of at least one of absorbing material and areflective material.
 9. The method of claim 7, wherein the concealingfeature comprises a mask layer of at least one of carbon black material,a dye, chromium, and molybdenum.
 10. The method of claim 7, wherein theconcealing feature comprises a metal film so as to form an etaloncomprising the metal film and the at least one reflecting element. 11.The method of claim 10, wherein the etalon has a thickness that causesetalon to reflect a color.
 12. The method of claim 1, wherein formingthe at least one reflecting element comprises forming a shaped basestructure on the substrate, and depositing a reflecting material on theshaped base structure.
 13. The method of claim 1, further comprisingforming a cavity in the substrate, and forming the at least onereflecting element substantially in the cavity of the substrate.
 14. Themethod of claim 1, wherein forming the at least one reflecting elementcomprises depositing a layer of reflecting material on the substrate andsurface treating said layer.
 15. The method of claim 1, wherein formingthe at least one reflecting element comprises depositing a compositematerial on the substrate surface, wherein the composite materialcomprises reflective particles suspended in a substantially transparentmaterial.
 16. The method of claim 15, wherein the composite material isdeposited at discrete locations on the substrate surface so as to form aplurality of reflecting elements.
 17. A spatial light modulatorfabricated by the method of claim
 1. 18. A method of backlighting aninterferometric modulator array, comprising: positioning a light sourceproximate a first side of the interferometric modulator array; andreflecting light from the light source to a second opposite side of theinterferometric modulator array with one or more reflecting elementspositioned between a substrate and a plurality of interferometricmodulator elements formed on the substrate.
 19. The method of claim 18,wherein the light is reflected with a plurality of discrete reflectingelements.
 20. The method of claim 18, wherein the light is reflectedwith one or more reflecting elements having sloped surfaces.
 21. Themethod of claim 18, wherein the light is reflected with one or moreconvex reflecting elements.
 22. The method of claim 18, wherein thelight is reflected with one or more concave reflecting elements.
 23. Themethod of claim 18, wherein the light is reflected with one or morereflecting elements comprising at least one of aluminum, silver,titanium, gold, and copper.
 24. The method of claim 18, wherein thelight is reflected with one or more reflecting elements, and wherein themethod further comprises masking the one or more reflecting elements tohide the reflecting element from view.
 25. The method of claim 24,wherein masking comprises forming at least a portion of an etalonbetween the one or more reflecting elements and a viewer.